This invention relates to a zoom or variable focal length lens and, more particularly, to a multi-element zoom lens whose focal length is varied in response to a desired magnification change by varying the pressure of a gas enclosed between at least two of the lens elements.
As is known in the art, multi-element zoom lens typically achieve a variation in focal length by mechanically varying the spacing between elements or groups of elements. U.S. Pat. Nos. 3,630,599 and 3,640,605 are representative of such lenses. These lenses require very precise movement of lens elements or lens groupings typically involving use of cams and related linkages. These demands result in relatively high cost.
A technique for varying focal length in a compound lens by varying gas pressure at the inter-lens media has been described by James D. Rees in an abstract entitled "Technique for Varying Focal Length of a Lens" published in Xerox Disclosure Journal, Vol. I, No. 11/12. Applicants have discovered that a preferred lens construction, when utilized with a preferred group of gases in an enclosed cavity between lens elements provide an exemplary variable magnification lens.